For example, in a radio communication system, a radio transmission apparatus for transmitting a radio signal amplifies a high frequency signal by a high output amplifier (power amplifier), so as to transmit from an antenna. The power amplifier has a gain characteristic which varies with temperature, and is decreased as the temperature becomes high. Therefore, in order to maintain a constant signal gain irrespective of a thermal change, the signal gain being input to the power amplifier is adjusted by a gain temperature compensation circuit, and thereby temperature compensation is performed.
FIG. 1 is a diagram illustrating an exemplary configuration of the conventional gain temperature compensation circuit. FIG. 1A is an exemplary circuit configuration, and FIG. 1B is a diagram illustrating the attenuation amount characteristic thereof. As shown in FIG. 1A, the gain temperature compensation circuit has a configuration in which a thermistor, of which impedance varies with temperature, is connected to a resistance element having a fixed impedance. For example, in the circuit configuration shown in FIG. 1A, by appropriately modifying the resistance value, it is possible to design to obtain a desired compensation value of the attenuation amount (gain) relative to a temperature change in a predetermined temperature range (for example, from −40° C. to 100° C.).
The following patent document 1 describes a method for compensating the temperature characteristic of a solid amplifier by varying the reference voltage of an error amplifier according to a varied resistance value of a thermistor.
[Patent document 1] The official gazette of the Japanese Unexamined Patent Publication No. Sho-53-113459.
However, in the conventional gain temperature compensation circuit, when it is intended to secure a constant amount (10 dB, for example) of a variation width (thermal inclination) of the attenuation amount (gain) in a predetermined temperature range, there is a problem that the attenuation amount at a normal temperature (in the vicinity of 25° C.) becomes relatively large, and accordingly, a large loss of power is produced. For example, in FIG. 1B, the attenuation amount at the normal temperature (in the vicinity of 25° C.) becomes on the order of approximately 10 dB, and also, a minimum attenuation amount (at 100° C.) becomes approximately 6 dB.
Further, since the conventional gain temperature compensation circuit is integrated into a chip, if it is desired to modify the thermal inclination of the attenuation amount in a predetermined temperature range, it is necessary to change the overall components in the gain temperature compensation circuit.
There is a known means for controlling the attenuation amount by voltage control. However, because the voltage control according to temperature is required, there are defects that the circuit becomes large in scale, and that a power supply for the control becomes necessary.